1. Field of Invention
This invention relates to data transmission over wireless networks. More specifically, the invention relates to reducing the impact of wireless channel instability on data streams by selecting data packets for transmission based on priority of the data packets.
2. Description of Related Art
When a video data packet is delivered over a network, it typically shares the link with data packets and other audio/video data streams. As a result, if the available bandwidth is lower than that necessary to transmit the video data, long packet delay or even packet loss results. Various approaches have been proposed for adaptively transmitting and playing-out the video data based on network conditions to handle this type of situation and to reduce the impact of packet loss on video data quality.
In one conventional method, the play-out time at the player's end may be adjusted within a small range based on information about delay and the amount of data in a client buffer to prevent potential play-out discontinuity. See R. Ramjee, J. Kurose, D. Towsley and H. Schulzrinne, “Adaptive Playout Mechanisms for Packetized Audio Applications in Wide-area Networks,” Proceedings IEEE INFOCOM '94, Toronto, Canada, 12-16 Jun. 1994, pp. 680-88 and M. C. Yuang, P. L. Tien and S. T. Liang, “Intelligent video smoother for multimedia communications,” IEEE Journal on Selected Areas in Communications, February 1997, vol. 15, pp. 136-46.
Another conventional method implements an adaptive forward error control algorithm at a network node to reduce the packet loss rate. See J. C. Bolot and T. Turletti, “A Rate Control Mechanism for Packet Video in the Internet,” Proceedings IEEE INFOCOM '94, Toronto, Canada, 12-16 Jun. 1994, pp. 1216-23 and J. C. Bolot and T. Turletti, “Adaptive Error Control For Packet video in the Internet,” Proceedings of International Conference on Image Processing, Lausanne, Switzerland, September 1996, pp. 25-28.
Additionally, it is conventionally known that video data encoded using one standard may be transcoded to another standard that requires less bandwidth, thereby diminishing the problems of packet loss and diminished quality. See S. Achraya and B. Smith, “Compressed domain transcoding of MPEG,” Proceedings IEEE International Conference on Multimedia Computing and Systems, Austin, Tex., June 1998, pp. 295-304.
In another conventional video data transmission method, the output rates are adjusted based on feedback information about the network at the video data source. See J. C. Bolot and T. Turletti, “A Rate Control Mechanism for Packet Video in the Internet” and “Adaptive Error Control For Packet video in the Internet”, referenced above. In particular, for real time video data transmission, parameters in the coding algorithm may be adjusted to generate video data at different rates. See E. Amier, S. McCanne and R. Katz, “Receiver-driven bandwidth adaptation for light-weight sessions,” Proceedings ACM Multimedia 97, Seattle, Wash., USA, November 1997, pp. 415-26, B. Belzer, J. Liao and J. D. Villasenor, “Adaptive video coding for mobile wireless networks,” Proceedings of 1st International Conference on Image Processing, Austin, Tex., USA, November 1994, pp. 972-76, and H. Kanakia, P. P. Mishra, and A. R. Reibman; “An adaptive congestion control scheme for real time packet video transport,” IEEE/ACM Transactions on Networking, December 1995, vol. 3, pp. 671-82. If the video data is pre-encoded, bit-streams may be scaled by cutting high frequency components, by requantization, or by re-encoding reconstructed pictures. See A. Eleftheriadis and D. Anastassiou, “Meeting arbitrary QoS constraints using dynamic rate shaping of coded digital video,” Proceedings of the 5th International Workshop on Network and Operating system support for Digital Audio and Video, Durham, N.H., USA, April 1995, pp. 95-106, S. Jacobs and A. Eleftheriadis, “Real-time dynamic rate shaping and control for Internet video applications,” 1997 IEEE First Workshop on Multimedia Signal Processing, Princeton, N.J., USA, June 1997, pp. 558-63 and H. Sun, W. Kwok and J. Zdepski, “Architectures for MPEG compressed bitstream scaling,” IEEE Transactions on Circuits and Systems for Video Technology, April 1996, vol. 6, :191-9.
However, these conventional methods are generally only marginally effective. Moreover, these conventional methods are even less effective in a wireless network and are not readily useful with smoothed video transmission.